LPI2C Filter

[GXY]

I want to know how to use LPI2C filtering, including SCL filtering and SDA filtering. I use one S32K144 development board as the host and the other as the slave. Both sides set the parameters of the SCL and SDA filtering functions to the maximum (0xF), and then the host receives data and sends data from the machine. Normally, the data can be received correctly. But I used FLEXIXO's open drain output to output a 2M waveform and connected it to the SDA. This clutter was started when the third data was received, but the host did not filter out the waveform and used it as a stop condition and stopped data transmission. When I looked up the status of the register, I found that the flag bit of the host arbitration failure was set up, and the flag bit of the slave repeated starting condition was also set up, which proved that the filtering function did not work, because the manual said that LPI2C could ignore the configured waveform with a smaller cycle, and the waveform below 1.875us should be ignored according to my configuration, but the 2M waveform, that is, (500ns) waveform was not filtered out, so I was confused about the use and understanding of this function.

[PavelL]

Hello @GXY ,

This is a very interesting and well-constructed experiment that highlights the practical limitations of LPI2C glitch filtering on the S32K144.

First, I recommend measuring the actual shape of the interfering signal on the SDA line using an oscilloscope - especially the rise and fall times. Even if the pulse duration is below the configured filter threshold, slow edges or voltage levels crossing the digital threshold may still be interpreted as valid transitions.

Additionally, please ensure that both the master and the slave have glitch filtering enabled, ideally with the same filter settings. While the master typically initiates and controls the communication, the slave's interpretation of the bus state can also be affected by noise, especially during repeated start or stop conditions.

Best regards,

Pavel